Killifish: Species, Care, Size, Breeding, Diet & Water Parameters

Killifish fall into two broad ecological types:

Permanent-water species live in streams and stable aquatic zones where they spawn year-round on fine-leaved plants or tangled roots as adhesive or plant spawners. These tend to be less demanding in captivity.

Annual killifish inhabit seasonal pools in regions with dramatic dry/rainy cycles. When water disappears, adult fish die, but their eggs survive buried in the mud for months or even years. The next rainfall triggers hatching-and remarkably, some eggs from the same clutch may wait until the second or third rainy season to emerge. This survival strategy ensures the species persists even if a single rainy season fails. Annual genera include Cynolebias, Nothobranchius, and Pterolebias spp.

How Hard Are Killifish to Keep?

The difficulty of keeping killifish depends almost entirely on species selection. Since killifish occupy wildly different biotopes-from cool highland streams to warm coastal swamps to brackish estuaries-care requirements vary dramatically. There is no one-size-fits-all killifish setup.

Common beginner-friendly species (like the Common Lyretail and Banded Killifish) are quite forgiving and can thrive in modest 10-20-gallon tanks with basic care. However, specialized species like the Redtail Notho or Longfin Killie demand species-only setups with exacting water chemistry and seasonal water-level manipulation.

Water Chemistry and Temperature Essentials

Most killifish prefer soft, slightly acidic water:

• pH: 6.0-6.5 (generally ideal)

• Hardness: 50-100 mg/L (soft)
• Temperature: 64-86°F (18-30°C) depending on species-cool-water species like Palmqvist's Notho demand 64-68°F, while tropical species need 73-79°F

A few exceptions exist: Lake Tanganyikan species like Lamprichthys tanganicanus require hard, alkaline water. Always verify the exact parameters for your chosen species before setup.

Tank Setup and Behavioral Requirements

All killifish share several common needs:

• Dense planting with fine-leaved plants (Java Moss is ideal) for spawning sites and refuges

• Tight-fitting cover glass-killifish are exceptional jumpers and will escape unguarded tanks
• Spawning substrate: fine-leaved plants for plant spawners; peat fiber base for substrate spawners
• Low light (especially for Banded Panchax and other surface swimmers)

• Minimal current-killifish are adapted to still pools and slow streams

Feeding and Diet Challenges

This is where many new killifish keepers encounter their biggest hurdle: most killifish prefer live foods and are reluctant or unwilling to eat standard dry diets. In the wild, they feed on small invertebrates-insects, crustaceans, and zooplankton.

Successful diets include:

• Live foods (primary): brine shrimp nauplii, daphnia, small mosquito larvae, micro-worms, vinegar eels
• Frozen alternatives: freeze-dried items and frozen brine shrimp (second choice, not ideal)

• Prepared dry foods: many species reject these entirely; only experiment if live foods are unavailable

Plan your setup before acquiring killifish if you cannot easily source live cultures. Breeding your own brine shrimp or daphnia is cost-effective for frequent feeders.

Lifespan: Why Killifish Don't Live Long

One of the biggest surprises for new killifish keepers is their short lifespan. Even under optimal aquarium conditions, most killifish live only 1.5 years on average. Depending on the species:

• Short-lived annual fish (Cynolebias, Nothobranchius, Pterolebias) often live 12 months or less
• Moderate-lived species (Aphyosemion, Epiplatys) typically 2-3 years
• Longer-lived species (Fundulopanchax) may reach 4-5 years

This short lifespan is not a failure of care-it's part of their natural biology. Annual species evolved to live fast, grow rapidly, and reproduce before their pools dry. Even in captivity, they maintain this accelerated lifecycle. Plan your breeding efforts around this timeline; don't expect to maintain a single brood for years.

Sexing Killifish: Males vs. Females

Sexing is straightforward and reliable. Males have more pointed, elaborate fins (dorsal, anal, and caudal) and are typically far more colorful. Females have rounded fins and duller coloration-often drab brown or grey. This sexual dimorphism is consistent across nearly all killifish species and is visible even in juveniles as they mature.

Killifish in Community Tanks

Most killifish are not suitable for community tanks. They are predatory fish that view any smaller fish or invertebrate as food. Some species, notably the Striped Panchax (Aplocheilus lineatus), can coexist in a community if all other fish are distinctly larger and peaceful. However, even then, conflicts may arise.

Aggressive species like the Blue Gularis or Gunther's Nothobranch must be kept in species-only setups with multiple females and a single male. Males of the same or opposite sex will fight unless the tank is very large (20+ gallons) with abundant plants and hiding spaces.

Popular Killifish Species & Care Profiles

Common Lyretail - Aphyosemion australe

Origin: West Africa (Gabon, Cameroon, Zaire)
Size: 2.5 inches (6 cm)
Temperament: Peaceful and social
Temperature: 64-75°F (18-24°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Males display highly variable but striking coloration with elaborate fins; the upper body stripe is darker and more prominent than the lower. Females are duller. They are excellent breeders, spawning among plants over several days. For breeding, house multiple males with a single female; eggs hatch in about three weeks. This is an ideal beginner species.

Banded Killifish - Aphyosemion bitaeniatum

Origin: West Africa (coastal Nigeria, Benin, Togo)
Size: 2 inches (5 cm)
Temperament: Males quarrelsome (must be separated)
Temperature: 72-75°F (22-24°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Males are exceptionally colorful with a tall dorsal fin, often red-dominated with two dark side stripes. Females are dull brown. Males fight viciously, so keep only one male with two females. Spawning occurs among plants. This species is slightly more aggressive than the Common Lyretail but remains manageable for hobbyists.

Steel-Blue Killifish - Fundulopanchax gardneri

Origin: West Africa (Nigeria, western Cameroon)
Size: 3 inches (7.5 cm)
Temperament: Males quarrelsome
Temperature: 72-79°F (22-26°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Males are brilliant blue with red spotting along the flanks; females have brown dots and duller fins. This species does not require brackish water-a plus for simplicity. They spawn on fine-leaved plants or spawning mops, with fry hatching in about two weeks if the tank remains full.

Red-Striped Killifish - Aphyosemion striatum

Origin: West Africa (pools and swamps, northern Gabon)
Size: 2 inches (5 cm)
Temperament: Non-aggressive
Temperature: 64-72°F (18-22°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5); slightly brackish preferred
Diet: Live foods and prepared diets

Males display bright red horizontal stripes on a blue background; females are dull golden-brown with rounded fins. They thrive in heavily planted tanks with Java Moss as spawning substrate. Tank cover is essential due to their jumping ability.

Two-Striped Killifish - Aphyosemion bivittatum

Origin: West Africa (Cameroon, Nigeria, Togo)
Size: 2 inches (5 cm)
Temperament: Peaceful
Temperature: 72-75°F (22-24°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Similar to the Common Lyretail in both appearance and care, with males displaying elaborate fins and variable but attractive coloration. Females are duller. Spawning is prolonged (several days) among plants, with eggs hatching in three weeks. Excellent for community-style species setups with multiple males and females.

Blue Gularis Killifish - Fundulopanchax sjostedti

Origin: West Africa (shallow waters, Ghana, Cameroon, Nigeria)
Size: 5 inches (13 cm)-largest common species
Temperament: Relatively aggressive
Temperature: 73-79°F (23-26°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Males vary from yellowish to greenish-blue on the flanks. Keep only one male with several females and a peat substrate since they are substrate spawners. After spawning, remove adults, drain the tank, carefully extract the egg-laden peat, and allow it to partially dry (but not powdery). Refill with fresh substrate and peat; eggs will eventually hatch and fry can be reared on brine shrimp.

Walker's Aphyosemion - Fundulopanchax walkeri

Origin: West Africa (southern Ghana, southeastern Ivory Coast)
Size: 2 inches (5 cm)
Temperament: Aggressive and active
Temperature: 68-73°F (20-23°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0-6.5)
Diet: Live foods and prepared diets

Stunning bluish flanks with red spots and yellowish fins. They spawn either on plants or in a peat base. If using peat, remove and store it in a warm plastic bag so it partially dries for about six weeks; eggs will then hatch rapidly when rewet.

Palmqvist's Notho - Nothobranchius palmqvisti

Origin: East Africa (coastal Kenya, Tanzania)
Size: 2 inches (5 cm)
Temperament: Aggressive
Temperature: 64-68°F (18-20°C) - one of the coolest-water killifish
Water: Soft (50-100 mg/L), acidic (pH 6.0); slightly brackish preferred
Diet: Small live foods and prepared diets

Males have a bluish body with red mesh-like patterning; females are smaller and duller. For breeding, use a small aquarium half-filled with water and a peat base. Offer abundant live foods and allow water to evaporate naturally; the falling level triggers spawning. This species is an excellent introduction to annual killifish for dedicated hobbyists.

Korthaus' Notho - Nothobranchius korthausae

Origin: East Africa (swamp areas, Mafia Island, Tanzania)
Size: 2.5 inches (6 cm)
Temperament: Aggressive
Temperature: 73-79°F (23-26°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0)
Diet: Small live foods and prepared diets

Several color morphs exist: red-tailed forms (with either blue or brown bodies) and brown morphs. Males are always brighter than females. Water chemistry is crucial for these annual species. They can live a couple of years in captivity-longer than many annual killifish.

Gunther's Nothobranch - Nothobranchius guentheri (Redtail Notho)

Origin: East Africa (Mombasa, Kenya, to Pangani River, Tanzania, and Zanzibar)
Size: 2 inches (5 cm)
Temperament: Aggressive
Temperature: 73-79°F (23-26°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0)
Diet: Small live foods

Highly colorful and variable, these fish should be kept in groups of one male and several females. They spawn in peat and often die soon after-this is natural behavior for annual killifish. To hatch eggs, employ the "dry-wet-dry" cycle: dry the peat fully, rewet it, dry again, then place in a tank. Some eggs only hatch on second contact with water, a survival strategy that protects wild populations from total wipeout if a pool dries prematurely. This species demands experience and dedication.

Banded Panchax - Epiplatys annulatus

Origin: West Africa (streams, Sierra Leone, Nigeria, Liberia, Guinea)
Size: 1.75 inches (4.5 cm) - among the smallest killifish
Temperament: Relatively peaceful
Temperature: 73-79°F (23-26°C)
Water: Soft (50-100 mg/L), acidic (pH 6.0)
Diet: Small live foods and prepared diets

Four broad dark bands separated by pale areas make them instantly recognizable. Males have more colorful fins and blue irises; females are plainer. Keep them in densely planted tanks with subdued lighting since they swim close to the surface. They spawn among vegetation or on spawning mops, and eggs hatch in about eight days without parental attention-they do not eat their own eggs.

Breeding Killifish: Eggs, Hatching, and the Annual Lifecycle

Plant Spawners vs. Substrate Spawners

Killifish employ two primary spawning strategies:

Plant spawners (Aphyosemion and Epiplatys species) lay adhesive eggs on fine-leaved plants or spawning mops. They spawn repeatedly over days or weeks, and fry can often remain in the tank if the adult diet is adjusted to exclude very small pieces. Eggs hatch within 2-3 weeks.

Substrate spawners (Nothobranchius, Cynolebias, and Pterolebias species, plus some Fundulopanchax) bury their eggs in soft peat or mud. Adults must be removed after spawning, and the egg-laden peat dried partially (not completely desiccated) for weeks or months before reflooding to trigger hatching. This mimics the natural cycle of seasonal pools.

The Annual Killifish and the Dry-Wet Cycle

Annual species like Nothobranchius are the most specialized breeders. Their eggs can survive months of burial in dried mud, and some eggs employ a remarkable strategy: they won't hatch on first contact with water. Instead, they require multiple wet-dry cycles. This "diapause" ensures that if a pool refills briefly then dries again (common in seasonal climates), not all fry hatch into a doomed temporary pool.

To breed annual killifish:

• Set up a small aquarium (5-10 gallons) half-filled with 2-3 inches of peat substrate
• Introduce one male and several females
• Provide abundant small live foods
• Allow water to evaporate gradually (do not top off); as the level drops, spawning is triggered
• Once females appear spent, carefully drain the tank and remove the peat
• Place peat in a plastic bag and store it warm (68-75°F) in a dark space for 4-8 weeks
• Partially dry the peat (it should be damp but not saturated) and store for another 2-4 weeks
• Rewet the peat in a small tank; eggs should begin hatching within days
• Feed fry brine shrimp nauplii or liquid fry food immediately

Rapid Fry Development

Young killifish grow surprisingly fast, fueled by their short natural lifespan. Fed abundantly on live foods, they can reach maturity (and spawning size) in as little as 6-8 weeks. This rapid development allows hobbyists to achieve multiple generations per year from a single pair.

Common Mistakes and Troubleshooting

No spawning despite compatible pairs: Killifish often need a specific environmental trigger-falling water level, water change, temperature drop, or high live-food availability. Try water changes or gradual water removal for substrate spawners. For plant spawners, add more plants and live food.

Eggs fungus or fail to hatch: In plant spawners, add a few drops of methylene blue to the water containing eggs, or remove eggs to a separate tank with gentle aeration. For peat eggs, ensure partial drying is achieved; fully wet peat can cause mold.

Fry die without obvious cause: Killifish fry are tiny and require live foods or extremely fine prepared foods. Brine shrimp nauplii are reliable; dried food alone usually fails. Ensure adequate feeding 3-4 times daily.

Adults refuse to eat: Try multiple live-food cultures. If the fish are new arrivals, allow 1-2 weeks of acclimation. Blanched vegetables like spinach occasionally help (though killifish rarely accept them). Never force a diet change-some individuals will starve rather than adapt.

High aggression in pairs: For quarrelsome species, use a tank divider to separate males, or ensure a 1:3 or 1:4 male-to-female ratio with abundant plants and space.

Selecting Your First Killifish

If you are new to killifish, start with forgiving, affordable species that tolerate modest setups:

• Common Lyretail (Aphyosemion australe) - peaceful, easy to breed, widely available
• Banded Killifish (Aphyosemion bitaeniatum) - slightly aggressive but manageable
• Banded Panchax (Epiplatys annulatus) - tiny, peaceful, and engaging

Avoid annual killifish (Nothobranchius, Cynolebias) and highly specialized species initially. Once you are confident in water chemistry, live-food culture, and breeding logistics, expand to more challenging species.

Killifish reward patience and attention with stunning colors, fascinating behavior, and the satisfaction of successfully breeding fish in your own home-all without needing an expensive, sprawling aquarium setup.